The removal of sulfur from distillate fractions by a catalytic reaction with hydrogen to form hydrogen sulfide is widely applied in petroleum refining. In commercial processes, active catalysts are typically employed in fixed bed reactors with continuous mass transfer through the reactor for removal of sulfur from distillate fractions and light cycle oil fractions, with the desulfurized product used for blending highway diesel fuels having a limited sulfur content. For example, it is known to desulfurize distillates and light cycle oils containing from about 0.2 to about 1.2 weight percent sulfur to a level of about 0.05 weight percent sulfur in the presence of catalyst which comprise alumina, cobalt and molybdenum.
It is also known in the art that the activity of such catalysts, used in desulfurization, will decline to an ineffective level after a period of time which is highly dependent on process conditions and on the sulfur species present in the oil being treated. The decline in activity is believed to be due to the formation of carbon on the catalyst, such that a higher reaction temperature is required to maintain a desired degree of desulfurization as the catalyst activity declines. Since desulfurization catalyst life is dependent essentially on process conditions and to a large extent on the boiling point distribution of sulfur species present in the oil, both of which can change during a typical commercial run, a reliable prediction of catalyst life has been extremely difficult. Accordingly, it has been necessary to periodically regenerate or replace catalyst to insure acceptable catalyst activity, and suspend production during the regeneration or replacement operation, even though useful levels of activity remained on the catalyst being replaced or regenerated.
Accordingly, it is a primary object of this invention to accurately predict life of a catalyst in a distillate or LCO hydrodesulfurization operation with the prediction based on a computer simulation.
It is a more specific object of this invention to predict the temperature-time profile of a catalyst HDS reaction for various process and feed conditions.
It is another object of this invention to provide substantial savings in a petroleum refining process operation by providing guidance for refiners in avoiding premature regeneration or replacement of catalyst in a distillate HDS process.
Another objective of this invention is to provide guidance for refiners in evaluating future feedstocks for economical HDS processing.
Still another object of this invention is to predict process conditions for deep desulfurization operations of existing units.
A further object of this invention is to provide data for designing, sizing and costing new units for deep desulfurization.